Nuclear reactors of the pressurized water type make use of high velocity water flow in order to remove the heat from the fuel rods in the reactor core. The cooling water travels to the core through a variety of passages one of which is immediately adjacent to the edge of the reactor core. The material separating core coolant from the incoming coolant is stainless steel plate approximately 2 inches thick, and is known as the Baffle Plate. The pressure of the water outside the baffle may be 30 pounds per square inch higher than that within the reactor core. Occasionally, there are gaps between the various plates which make up the core baffle. The differential water pressure between the outside of the baffle and the inside cause the water to flow rapidly through these gaps. This water flow is referred to as a "water jet" and since the reactor core is essentially full of fuel rods the water jet impinges on or very near a fuel rod. The usual water flow within a reactor core is bottom to top, parallel to the fuel rods. The baffle gap induced jet flow is perpendicular to the usual water flow. When the baffle jet strikes the fuel rod from the side it tends to induce a vibration into the fuel rod. This vibration tends to cause excessive wear on the fuel rods where they contact their normal support points which are called spacers. This type of wear is known as fretting and may proceed completely through the fuel rod cladding which results in escape of fission products from the nuclear fuel into the reactor cooling water. Fission products in the cooling water make normal reactor maintenance more difficult and much more expensive to the utility. Attempts at preventing or closing the baffle gaps have not been satisfactory. Some utilities have considered rerouting the cooling water prior to entering the core, so as to reduce the differential pressure which causes the jetting. This rerouting, however, is extremely expensive and requires a lengthy reactor shutdown.